JOURNAL OF FUEL CHEMISTRY AND TECHNOLOGY Volume 40, Issue 1, January 2012 Online English edition of the Chinese language journal Received: 15-Aug-2011; Revised: 01-Dec-2011 * Corresponding author. Tel: 605-3688210; E-mail: noorasmawati_mzabidi@petronas.com Foundation item: Supported by the Ministry of Science, Technology and Innovation (E-Science Fund, 03-02-02-SF0036), Ministry of Higher Education Malaysia (FRGS/2/2010/SG/UTP/02/3) and Universiti Teknologi PETRONAS (31/09.10).. Copyright  2012, Institute of Coal Chemistry, Chinese Academy of Sciences. Published by Elsevier Limited. All rights reserved. RESEARCH PAPER Cite this article as: J Fuel Chem Technol, 2012, 40(1), 4853 Effect of niobium promoters on iron-based catalysts for Fischer-Tropsch reaction Sardar ALI 1 , Noor Asmawati MOHD ZABIDI 2, *, Duvvuri SUBBARAO 1 1 Department of Chemical Engineering, Universiti Teknologi PETRONAS, Bandar Seri Iskandar, 31750 Tronoh, Perak, Malaysia 2 Department of Fundamental and Applied Sciences, Universiti Teknologi PETRONAS, Bandar Seri Iskandar, 31750 Tronoh, Perak, Malaysia Abstract: Niobium-promoted Fe/CNT catalysts were prepared using the wet impregnation method. The samples were characterized by nitrogen adsorption, H 2 -TPR, TPD, XRD and TEM. The Fischer-Tropsch Synthesis (FTS) was carried out in a fixed-bed microreactor at 220°C, 1 atm and H 2 /CO=2 for 5 h. Addition of niobium into Fe/CNTs increased the dispersion, decreased the average size of the iron oxide nanoparticles and the catalyst reducibility. The niobium-promoted Fe catalyst resulted in appreciable increase in the selectivity of C 5+ hydrocarbons and suppressed methane formation. These effects were more pronounced for the 0.04%Nb/Fe/CNT catalyst, compared to those observed from other niobium compositions. The 0.04%Nb/Fe/CNT catalyst enhanced the C 5+ hydrocarbons selectivity by a factor of 67.5% and reduced the methane selectivity by a factor of 59.2%. Key Words: CNTs; iron; niobium; Fischer-Tropsch synthesis Fischer-Tropsch synthesis (FTS) is a process that deals with the conversion of syngas derived from coal, biomass and natural gas into diesel fuels consisting of paraffins, olefins, alcohols and aldehydes with a high cetane number and is environmentally friendly [1] . Owing to limited petroleum reserves and environmental restrictions, FTS is gaining more attention nowadays. All the group VIII elements show considerable activity for this process [2] . Among them Co, Fe and Ru display the highest activity. Fe- and Co-based catalysts are commonly used in industries for this process [3,4] . In many heterogeneous reactions, the active phase is dispersed on a support which not only acts as a carrier but may also contribute to the catalytic activity. Al 2 O 3, SiO 2 and TiO 2 are the commonly used supports [5,6] . The major drawback of these supports is their reactivity towards iron, which leads to the formation of mixed compounds possessing very high reduction temperatures. In order to overcome these problems, use of activated carbon as a catalytic support has been exploited as activated carbon is not only stable at high temperatures but also resistant to acidic and basic media. Carbon nanotubes (CNTs) out-performed activated carbon in terms of mechanical strength, porosity and thermal conductivity [7,8] . Besides metal-support interactions, porosity and mass transfer limitations, catalyst supports may also have considerable effects on the catalytic activity and selectivity [9–11] . CNT-based catalysts have considerable activity and stability in FTS, but at the same time, it was found to decrease the C 5+ selectivity and increase the methane production [12] . Mendes et al [13] found that niobium-supported Co catalysts are more selective to C 5+ hydrocarbons; however, reducibility and dispersion of these catalysts were found to be very low. Work on Nb-promoted CNT-supported iron catalyst has not been reported in the literature. In our present work, we have modified CNT-based iron catalysts by adding niobium as a promoter. The effects of incorporation of niobium on the physicochemical properties and FTS activity of the iron-based catalysts as well as the selectivity to hydrocarbons have been studied. 1 Experimental 1.1 Catalyst preparation All the catalysts were prepared using a wet impregnation method. Prior to metal loading, carbon nanotubes (CNTs), (purity >95%, CVD, length: 10–50 m, diameter: 10–25 nm, ILJIN Nanotech Co., Ltd) were functionalized and activated. In this process, the required amounts of CNTs were treated with 35% HNO 3 (Merck) for 16 h at 110°C followed by